1. Field of the Invention
This invention relates to a method for image registration for purpose of document authentication, and in particular, it relates to a method for image registration using barcodes printed on the document as markers.
2. Description of Related Art
A closed-loop process refers to printing an original digital document (which may include text, graphics, images, etc.), using the printed hardcopy of the document such as distributing it, copying it, etc., and then scanning a hardcopy of the document back into digital form. Authenticating a scanned digital document refers to determining whether the scanned document is an authentic copy of the original digital document, i.e., whether the document has been altered while it was in the hardcopy form. Various types of document authentication and alteration detection methods have been proposed. A goal in many document authentication methods is to detect what the alterations (additions, deletions) are. One type of document authentication method performs an image comparison of the scanned document with the original digital document. This is sometimes referred to as a pixel-based alteration detection method. In another type of document authentication method, data representing or relating to the document content are encoded in barcodes, and the barcodes are printed on the document itself to assist in document authentication later.